CNC machine tools combine the advantages of traditional automatic machine tools, precision machine tools and universal machine tools, and integrate high efficiency, high precision and high flexibility into one. The improvement of the technical level of CNC machine tools depends first on the improvement of feed and spindle drive characteristics and the expansion of functions.
Generally have the following requirements for servo:
(1) Forward and reverse operation
During machine tool work, the table may require forward or reverse movement at any time according to the shape of the machining track. At the same time, the conversion of electrical energy and mechanical energy between starting and braking during forward and reverse operation should be considered to achieve reliable fast braking.
(2) Wide high speed range
In order to adapt to different processing conditions, such as the material, type and size of the processed parts, as well as the type of tool and cooling method, etc., a wide speed range and excellent speed characteristics of the servo are required.
(3) High rigidity and high speed stability
The servo should keep the feed rate constant under different load conditions or cutting conditions. It is required that the servo has excellent static and dynamic load characteristics.
(4) Fast response and no overshoot
In order to ensure the accuracy of contour cutting shape and low surface roughness of the machined surface, the servo must have good fast response characteristics without overshoot.
(5) High precision
In order to meet the processing accuracy, the positioning accuracy and feed accuracy of the machine tool must be guaranteed, that is, the servo must have a high static resolution, and the dynamic characteristics should be at least a first-order error-free system.
(6) Low speed and large torque
The characteristics of machine tool processing are mostly cutting at low speed. It is required that the feed drive should guarantee the rated torque output at low speed, that is, the servo must have constant torque output.
In addition to the above-mentioned feed servo characteristics, the spindle servo as a speed regulating device should also have the following characteristics:
(1) High output power
In order to meet the requirements of productivity, the spindle should have more power than the feed.
(2) With constant torque section and constant power section
During the processing of the machine tool, the cutting force is very small at high speeds. In order to fully improve the efficiency of the motor, the field weakening control is generally implemented at the high speed of the motor to make the motor output power constant.
(3) With exact stop control.
The machine tool often requires that the spindle must stop at a fixed radial position during processing. Therefore, it is required that the servo has the function of accurately stopping at a preset position.
(4) Linkage between spindle and feed
In the thread processing of the machine tool, the linkage between the spindle and feed is required, so the spindle must have the same servo function as feed.
(5) Constant linear speed cutting control
When the machine tool is performing end face cutting, the linear speed of the contact point between the workpiece and the tool tip is often constant, so the spindle must have a uniform speed-up function.